Creep resistant chromium steel



United States Patent CREEP RESISTANT CHROMIUM STEEL Geolfrey T. Harris, Sheflield, and Henry C. Child, Rotherham, England, assignors to The Birmingham Small Arms Company Limited, Birmingham, England, a British company No Drawing. Application January 5, 1956 Serial No. 557,449

3 Claims. (Cl. nus-s1 This invention relates to ferritic chromium steels. Such steels have been used to a large extent in recent years for creep-resistant applications such as turbine and compressor discs in gas turbines. The normal procedure has been to harden and temper the alloy and it has been shown by numerous workers that the composition of the steel is critical if optimum properties are to be obtained, it being generally accepted that if the composition of the steel is such that it is not wholly austenitic-at the hardening or solution temperature, the final structure of the steel will be a tempered martensite with areas of free ferrite and if these areas of free ferrite are extensive, they have a deleterious effect on the creep strength and transverse ductility of the material.

v 2,905,577 Patented Sept. 22, 1959 Percent Carbon 0.05-0.33 Manganese v i Q 0.05-2.0 Nickel 0-4 Silicon 0.05-1.0 I Cobalt 0-4 I Chromium 9-20 Trungsten 03* Molybdenum; 0-3 Niobium and tantalum 0-2 Titanium 0-2 Vanadium 0-2 Nitrogen 0.0010.2 Boron 0005 *At least 0.7% total of these elements for adequate creep strengths.

In addition up to 0.5 total of any of the strongerdeoxidisers such as aluminium, cerium, magnesium could be present if desired but these are not essential.

Example of alloys within these ranges are:

0 Mn Si Cr Mo Nb V '1! N B W Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent It is an object of the present invention to obviate the close control of composition.

According to this invention chromium steels which are essentially ferritic (for example containing at least 60% ferrite) at normal solution or hardening temperatures (for example l000-1300 C.) and so do not harden on quenching, are subsequently treated to improve or provide creep strength.

The treatment referred to may consist of cold or Warm working the soft ferritic steel or by a combination of solution hardening and precipitation hardening of the material or by all three mechanisms.

Cold or warm working may comprise heating the solution treated material to the desired temperature within a suitable range, e.g. 20700 C., and then working it by rolling, stamping, pressing or any other means to a reduction in thickness or diameter of, for example 1% to 10%.

Solution hardening or precipitation hardening may be effected with the use of precipitation hardening additions, such for example, as molybdenum, tungsten, niobium, tantalum, titanium or other suitable known materials.

Further features of the invention will be apparent from the following description of detailed methods, given by way of example of carrying out the invention.

Steels suitable for cold or Warm working as above described may have any composition within the specification The above alloys tested at 30 tons/sq. in. at 500 the following figures:

C. gave For solution hardening and precipitation hardening materials the specification is as above described with the exception of:

Percent Molybdenum 0-6* Tungsten 0-6 Vanadium 0-2 Niobium and tantalum 02T Titanium 0 2? Solution hardening addition, totalling at least 1.5%.

tPrecipitation hardening addition. These steels may also be warm worked but satisfactory creep strength can be achieved without this process. Examples:

0 Mn Si Cr Mo W V Nb N B Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent WEX352 0. 05 0. 8 0. 3 13 1 1 0. 2 0. 6 0. 1 0. 01 WEX409 0. 05 0. 8 0. 3 13 2 2 0. 2 0. 5 0. 1 0. 01 WEX051 0. 05 0. 8 0. 3 13 2 2 0. 2 0. 25 0. 1 0. 01

The alloys are normally solution treated at 1000-1300 I (Land air, all or wateriquenched. .They aresuhsequently aged in the temperature range 500-700 C.

The above examples, when oil quenched at 1200" C., aged for 2.0 hours M650 and testede :30 DDS t i $50.01G.gawethetolldwingfigures: Y

What we 'claim is:

l. A normally non-handenahle chromium steel contain ing .at least 60% ferrite at 1000-1300 C., at least one element selected from the group consisting of 06% molybdenum, 0-6% tungsten and 0 2% vanadium where in the elements are present in'atotal amount'of at least 1.5% for the purpose of solution treatment wherein said steel has been treated to improve creep strength by the steps comprising solution treating the steel at a temperature in the range of 1000-1300 C., quenching the steel for the purpose of e'fifecting solutiontreatment thereof and working the steel at a temperature the temperature range of 20-700 C. to reduce the thickness thereof substantially 1%10%.

'2. The steel .as defined in;.claim'1 containing at least one element selected from the group consisting of 0-2% titanium, and .0-.2% niobium and tantalum wherein said elements are present in an effective amount for producing precipitation hardening and wherein the steel has been treated to improve creep strength by the step comprising aging the steel in a temperature, range of 500-700 C. after the steel has been Worked to reduce the thickness thereof;

3. The steel as defined in claim 1 containing at least one-element selected from the "group consisting of 0 2% titaniumyand 0 2% niobium and tantalum wherein said elements are present in an effective amount ior producing precipitation hardening and wherein the steel has been treated to impress creep strength theneof .by the step comprising aging the steeliat a temperature range of 5 00-7 00 C. following quenching ofsaid steel and before working of said steel to reduce the'thickness thereof.

References Cited in the file of this patent 

1. A NORMALLY NON-HARDENABLE CHLORMIUM STEEL CONTAINING AT LEAST 60% FERRITE AT 1000*-1300*C., AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF 0-6% MOLYBDENUM, 0-6% TUNGSTEN AND 0-2% VANADIUM WHEREIN THE ELEMENTS ARE PRESENT IN A TOTAL AMOUNT OF AT LEAST 1.5% FOR THE PURPOSE OF SOLUTION TREATMENT WHEREIN SAID STEEL HAS BEEN TREATED TO IMPROVE CREEP STRENGTH BY THE STEPS COMPRISING SOLUTION TREATING THE STEEL AT A TEMPERATURE IN THE RANGE OF 1000*-1300*C., QUENCHING THE STEEL FOR THE PURPOSE OF EFFECTING SOLUTION TREATMENT THEREOF AND WORKING THE STEEL AT A TEMPERATURE WITHIN THE TEMPERATURE RANGE OF 20*-700*C. TO REDUCE THE THICKNESS THEREOF SUBSTANTIALLY 1%-10%. 